1. Field of the Invention
The present invention relates to a sheet feeder and an image forming apparatus, and more particularly, to a sheet feeder which can detect the stacking amount of sheets contained in the sheet feeder, and an image forming apparatus including the same.
2. Description of the Related Art
Conventionally, in an image forming apparatus such as a printer, a facsimile machine, or a copying machine, there has been known a method of detecting that the amount of sheets stacked in a stacking tray becomes smaller using the rotation position of an intermediate plate which raises the sheets (Japanese Patent Application Laid-Open No. H06-179544).
In an image forming apparatus, for example, sheets are pushed up by rotating an intermediate plate which is rotatably supported by a stacking tray, and first, the presence or absence of sheets stacked on the intermediate plate is detected by a sheet presence or absence detection sensor. When there is no sheet, the image forming apparatus ends feeding operation. When sheets are stacked, the upper surface of the sheets is detected by an upper surface detection sensor so that the sheets which are pushed up are kept at a predetermined height. Further, a remaining amount detection sensor detects the stacking amount of the sheets based on the rotation position of the intermediate plate or the like.
In the conventional image forming apparatus, in detecting the stacking amount of the sheets stacked in the stacking tray, the three sensors, that is, the sheet presence or absence detection sensor, the upper surface detection sensor, and the remaining amount detection sensor are required. Therefore, space for the sheet presence or absence detection sensor, the upper surface detection sensor, and the remaining amount detection sensor is necessary, which inhibits downsizing of the image forming apparatus that is desired these days, and also, the need for the three sensors inhibits cost reduction of the image forming apparatus.